This is what we found on Wikipedia regarding the Hotel Lux:

Hotel Lux (Люксъ) was a hotel in Moscow during the Soviet Union, housing many leading exiled and visiting Communists. During the Nazi era, exiles from all over Europe went there, particularly from Germany. A number of them became leading figures in German politics in the postwar era. Initial reports of the hotel were good, although its problem with rats was mentioned as early as 1921. Communists from more than 50 countries came for congresses, for training or to work. By the 1930s, Joseph Stalin had come to regard the international character of the hotel with suspicion and its occupants as potential spies. His purges created an atmosphere of fear among the occupants, who were faced with mistrust, denunciations, and nightly arrests. The purges at the hotel peaked between 1936 and 1938. Germans who had fled Nazi Germany, seeking safety in the Soviet Union, were interrogated, arrested, tortured, and sent to forced labour camps. Most of the 178 leading German communists who were killed in Stalin's purges were residents of Hotel Lux.